Re: [PATCH] virtio-scsi: set dataplane_started to false upon failure

["Philippe Mathieu-Daudé" <philmd@oss.qualcomm.com>]

On 25/8/26 17:48, Stefan Hajnoczi wrote:
> Commit e24a47c5b73e ("virtio-scsi: do not use vring in dataplane") set
> dataplane_started to true when virtio_scsi_dataplane_start() fails. This
> is likely a typo since dataplane is not functional after failure.
> 
> The non-ioeventfd fallback is broken because dataplane_started is true
> after virtio_scsi_dataplane_start() failure. As a result, the following
> assertion failure occurs when a virtio-scsi device exceeds the open file
> descriptor ulimit when setting up notifiers (eventfds):
> 
>    $ ulimit -n 104 # exact number can vary based on QEMU version
>    $ qemu-system-x86_64 -M q35,accel=kvm -m 1G -cpu host -smp 14 \
>           --blockdev file,node-name=drive0,filename=test.img,cache.direct=on,aio=native \
>           --blockdev file,node-name=drive1,filename=data01.img,cache.direct=on,aio=native \
>           --device virtio-scsi-pci,id=virtio-scsi-pci0 \
>           --device scsi-hd,drive=drive0,bus=virtio-scsi-pci0.0 \
>           --device virtio-scsi-pci,id=virtio-scsi-pci1 \
>           --device scsi-hd,drive=drive1,bus=virtio-scsi-pci1.0
>    qemu: virtio-scsi: Failed to set guest notifiers (-24), ensure -accel kvm is set.
>    qemu: virtio_bus_start_ioeventfd: failed. Fallback to userspace (slower).
>    qemu-system-x86_64: ../hw/scsi/virtio-scsi.c:1017: virtio_scsi_reset: Assertion `!s->dataplane_started' failed.
>    Aborted                    (core dumped)
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Fixes: e24a47c5b73e ("virtio-scsi: do not use vring in dataplane")
> Buglink: https://redhat.atlassian.net/browse/RHEL-193328
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>   hw/scsi/virtio-scsi-dataplane.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>